Modern analog CMOS processes offer so-called “extended drain” high-voltage power MOS transistors that have up to 30V of maximum drain-to-source voltage. The admissible gate-to-source voltage is only 7 V. Other modern processes offer power DMOS transistors with a maximum drain-to-source voltage up to 60 V. In this case, the admissible gate-to-source voltage is limited to 16 V. With these transistors, inductive voltage-converters can be built for supply voltages above 10 V and even up to 20 V. A problem with these transistors is that their gates cannot be driven directly from the supply voltage since the maximum gate-to-source voltage is limited to a value considerably below the supply voltage.
A conventional approach to solve this problem is the use of a linear voltage regulator that provides a limited voltage for the gate drive circuits of the power transistors. Such a voltage regulator must deliver the full charging current for the gate of the power transistor. For large power transistors the gate charging current is on the order of one Ampère, although for a short duration of only a few nanoseconds. When other circuit blocks are also supplied from the voltage regulator, its output voltage must not drop when the power transistor is turned on, as this would cause disturbance of those circuit blocks. Therefore, the voltage regulator must have a large pass transistor. Alternatively, a buffer capacitor could be used but, in order to be effective, a buffer capacitor would be much bigger than the gate capacitance of the power transistor and could not be integrated. A requirement for an off-chip capacitor is often not acceptable. Also, when a voltage regulator is used, the gate charge current path contains the pass transistor of the regulator in series with the switching transistor of the gate drive circuit. For the same amount of effective resistance in the gate charge current path compared to a single switching transistor in that current path, each of the series-connected transistors must be two times the size of a single switching transistor.